Libyan government forces fire at ISIL positions on the outskirts of Sirte. /Reuters

The airstrikes were requested by the Libyan Government of National Accord (GNA), which is based in Tripoli and is supported by the United Nations, according to the Pentagon statement. The strikes were aimed at defeating ISIL “in its primary stronghold in Libya,” it said.

Cook didn’t describe the duration of the strikes, the type of aircraft used or whether they were land- or carrier-based. The initial U.S. assessment was that an ISIL tank and two vehicles were destroyed.

“Our assistance will be limited to strikes in this area” around Sirte, which government forces have been trying to retake since May, Cook said, adding the Libyan government “will be determining the pace” of U.S. airstrikes in the requests they make.

Sirte, 450 kilometers (280 miles) east of Tripoli, has been controlled by ISIL since June 2015, and has become a vital training camp for the terror organization.

Pro-GNA forces said on Aug. 2 they had gained full control of Al-Dollar, a central residential district in Sirte, after clashes that killed five of their members and wounded 17.

“GNA-aligned forces have had success in recapturing territory from ISIL thus far around Sirte, and additional U.S. strikes will continue to target ISIL in Sirte in order to enable the GNA to make a decisive, strategic advance,” the Pentagon statement said.

“These actions and those we have taken previously will help deny ISIL a safe haven in Libya from which it could attack the United States and our allies,” it added.